import turf from 'turf'

export default {

TILE_SIZE: 256,

/*

* 获取指定级别的瓦片数目

*/

_getMapSize(level) {

return Math.pow(2, level);

},

/**

* Convert a longitude coordinate (in degrees) to the tile X number at a

* certain zoom level.经度转瓦片列号

* @param longitude

* the longitude coordinate that should be converted.

* @param zoom

* the zoom level at which the coordinate should be converted.

* @return the tile X number of the longitude value.

*/

longitudeToTileX(longitude, zoom) {

let px = this.longitudeToPixelX(longitude, zoom);

return this.pixelXToTileX(px, zoom);

},

/**

* Convert a latitude coordinate (in degrees) to a tile Y number at a

* certain zoom level.纬度转瓦片行号

* @param latitude

* the latitude coordinate that should be converted.

* @param zoom

* the zoom level at which the coordinate should be converted.

* @return the tile Y number of the latitude value.

*/

latitudeToTileY(latitude, zoom) {

let py = this.latitudeToPixelY(latitude, zoom);

return this.pixelYToTileY(py, zoom);

},

/**

* Convert a latitude coordinate (in degrees) to a pixel Y coordinate at a

* certain zoom level.经纬度坐标(纬度)转屏幕像素坐标(Y)

*

* @param latitude

* the latitude coordinate that should be converted.

* @param zoom

* the zoom level at which the coordinate should be converted.

* @return the pixel Y coordinate of the latitude value.

*/

latitudeToPixelY(latitude, zoom) {

let sinLatitude = Math.sin(latitude * Math.PI / 180);

return (0.5 - Math.log((1 + sinLatitude) / (1 - sinLatitude)) / (4 * Math.PI)) * (this.TILE_SIZE << zoom);

},

/**

* Convert a longitude coordinate (in degrees) to a pixel X coordinate at a

* certain zoom level.经纬度坐标(经度)转屏幕像素坐标(X)

*

* @param longitude

* the longitude coordinate that should be converted.

* @param zoom

* the zoom level at which the coordinate should be converted.

* @return the pixel X coordinate of the longitude value.

*/

longitudeToPixelX(longitude, zoom) {

return (longitude + 180) / 360 * (this.TILE_SIZE << zoom);

},

/*

* 指定级别下，将宏观上的经度转换为对应列上的瓦片的像素矩阵列号(微观)

例如：鼠标点击地图，鼠标位置在点击的瓦片内的行列号(即使像素行列号)。根据该瓦片(png)和计算出的行列号，即可取得鼠标点击位置的像素值。

*/

_lngToPixelX(longitude, level) {

let x = (longitude + 180) / 360;

let pixelX = Math.floor(x * this._getMapSize(level) * 256 % 256);

return pixelX;

},

/*

* 指定级别纬度对应的像素行号

*/

_latToPixelY(latitude, level) {

let sinLatitude = Math.sin(latitude * Math.PI / 180);

let y = 0.5 - Math.log((1 + sinLatitude) / (1 - sinLatitude)) / (4 * Math.PI);

let pixelY = Math.floor(y * this._getMapSize(level) * 256 % 256);

return pixelY;

},

/**

* Convert a pixel X coordinate to the tile X number.

* 像素坐标X转瓦片行列号X

* @param pixelX

* the pixel X coordinate that should be converted.

* @param zoom

* the zoom level at which the coordinate should be converted.

* @return the tile X number.

*/

pixelXToTileX(pixelX, zoom) {

return Math.floor(Math.min(Math.max(pixelX / this.TILE_SIZE, 0), Math.pow(2, zoom) - 1));

},

/**

* Converts a pixel Y coordinate to the tile Y number.

* 像素坐标Y转瓦片行列号Y

* @param pixelY

* the pixel Y coordinate that should be converted.

* @param zoom

* the zoom level at which the coordinate should be converted.

* @return the tile Y number.

*/

pixelYToTileY(pixelY, zoom) {

return Math.floor(Math.min(Math.max(pixelY / this.TILE_SIZE, 0), Math.pow(2, zoom) - 1));

},

}